1. Field of the Invention
The present invention relates to a method for transmitting data in a radio frequency identification system (RFID system), which includes a reader and at least one transponder known as a tag, or for transmitting data between a reader and a remote sensor.
2. Description of the Background Art
Automatic identification methods, also known as Auto-ID, have become widespread in recent years in many service fields, in procurement and distribution logistics, in trade, in production, and in material flow systems. The goal of Auto-ID in this context is the comprehensive provision of information concerning persons, animals, objects and goods.
One example of such Auto-ID systems is the widely used chip card, in which a silicon memory chip is powered, read and if necessary reprogrammed by a reader by means of mechanical galvanic contact. In this context, the acquisition device is generally referred to as a reader regardless of whether it can only read data or can also write it.
In RFID systems, power can be supplied to the data carrier—the transponder—not only by galvanic contact, but also in a non-contact manner using electromagnetic fields in the radio frequency range.
RFID systems typically have two basic components, namely the transponder, i.e. an integrated circuit having a coupling element such as a dipole antenna as a transmitting and receiving device and also an electronic microchip, and a reader, which is typically a high-frequency module (transmitter/receiver) and likewise has a coupling element. The reader supplies the transponder, which as a rule does not have its own voltage supply, with energy and a clock; data are transmitted both from the reader to the transponder (forward link) and in the opposite direction (return link).
Such RFID systems, whose range is significantly greater than 1 m, use electromagnetic waves in the UHF and microwave regions. These systems mostly use a backscatter method, named for its physical principle of operation; in this method, a part of the energy arriving at the transponder from the reader is reflected (scattered back, hence backscattering) and may be modulated in the process in order to transmit data.
Especially in material flow systems, such as those known as supply chain systems, a great number of transponders can come together in the field of one reader, which must communicate with each individual transponder. In this regard, it may be the case that the individual transponders differ with regard to a protocol they support. This application can be addressed through the use of multi-protocol readers which sequentially try the possible protocols. At the same time, the transponders must be able to respond appropriately, i.e., a transponder must not answer when a protocol other than its own is used.
In any case, RFID systems or remote sensor systems are generally defined by a specific base protocol that is understood by all transponders or sensors. This base protocol is augmented by extensions in the address and/or parameter range and/or command sequences so that different protocol levels can be implemented in different transponders or remote sensors if necessary. This situation is to be expected when protocol extensions or reductions (e.g., to a minimal protocol) are possible. In this way, especially in open systems, there exists the danger that while the transponders or sensors are in principle capable of extracting a command from command data transmitted by a reader and translating it into a binary data stream, only a (sub) group of transponders or sensors can recognize and execute the command, while another (sub) group cannot. The same applies to transmitted command extensions such as the aforementioned parameter or address data.
The consequences of such compatibility problems can include disruption of the communication between the reader and the transponders or sensors, so controlled error handling is absolutely necessary for the described situation.
A method for this purpose is known from ISO 18000-6 FDIS 2003(E), Section 7.4.8, in which a transponder returns an error code to the reader upon detection of an error condition of the aforementioned type. This error code contains the coding “Unrecognized command received” (loc. cit., Table 27), which in the situation described above can have the result that one transponder executes the command and returns a corresponding positive response to the reader, while another transponder transmits the aforementioned error code. In this way, two data streams can be superimposed in the backscatter, which can make communication impossible or at least more difficult.
Furthermore, the aforementioned ISO standard also permits user-specific commands and corresponding parameter sets in the command vocabulary. If transponders or remote sensors of this type are present in an open Auto-ID system, the aforementioned problems will necessarily arise.
There are also conventional methods for data transmission in RFID systems, which allow decoded data to be sent back to the reader even during a running transmission of command data from the reader to the transponder through the forward link. In this way the reader can rapidly determine whether a transponder has detected a transmission error. However, the method does not encompass notifying the reader as to whether the command per se and/or its associated extensions are recognized by the transponder. Moreover, it must also be seen as a disadvantage that the cited method requires the reader to have full-duplex capability during the forward link (the connection from the reader to the transponder) and that the transponder must operate synchronously with the reader.